Solve for $a$ : $28 + a = -10$
Subtract $28$ from both sides: $ \begin{eqnarray} \\ 28 + a &=& -10 \\ \\ {-28} && {-28} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{28 + a} &\hphantom{=}& \hphantom{-10} \\ a &=& -10 {- 28} \\ \end{eqnarray} $ Simplify. $ a = -38$